Knitr: siunitx clashes with OutDec = ","

Question

I'm having the following problem.

I'm trying to type up something in Danish, which means I want a comma for the decimal mark. Usually I have no issues doing this, I simply set

<<>>=
   options(OutDec = ",")
@

However, in my current document this introduced an error I was having trouble locating at first. Specifically, I'd get an error message of the form ! Incomplete \iffalse; all text was ignored after line [x]. Playing around a bit, it seems the error arises from a clash with siunitx. Setting OutDec = "," appears to enclose numbers resulting from \Sexpr{} in \text{} while changing the decimal mark to a comma. Usually this isn't a problem, but \siunitx doesn't appear to like the combination of math mode and \text{}. At least, I get the relevant error message from the following MWE:

\documentclass{article}
\usepackage{siunitx}

\begin{document}
    $ \SI{\text{1}}{\meter} $
\end{document}

However, I'd rather like to continue being able to use \Sexpr{} within \SI{}{} and get the correct decimal mark.

Any ideas on how to fix this?

Answer 1

Why don't you use the following to get the correct decimal mark:

\documentclass{article}
\usepackage{siunitx}
\sisetup{output-decimal-marker = {,}}

\begin{document}
$\SI{1.5}{\meter}$
$\SI{1,5}{\meter}$ % ',' works, too
\end{document}